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Big impacts: The main messages from today’s big UN climate report

31 Mar 2014, 12:30

Roz Pidcock

A landmark new report on
climate change came out earlier today, looking at the impact of
past and future warming on ecosystems and human society. Here's our
rundown of the report's main messages, on everything from fisheries
to flooding.

We're already seeing the impacts of climate
change

That the planet is warming is not in doubt.
Global temperature has risen by0.85 degreesover the industrial period
(1880 to date). We're already seeing the impacts of this amount of
warming over much of the land and oceans.

The Summary for Policymakers (
SPM) says some risks of climate change are considerable at 1 or
2°C above preindustrial levels and that further warming will
"increase the likelihood of severe, pervasive, and irreversible
impacts."

Greater confidence in the extent and pace of
climate change since the last assessment report comes from having
more data and new ways of analysing earlier
measurements.

Our weather will get more extreme

Climate change is already leading to more hot
days and nights and fewer cold days and nights. Heatwaves have
become more common and more intense in the last half
century.

In general, wet places are set to get wetter,
and dry places to get drier. Some parts of the world are already
seeing more frequent and more serious drought, leading to a
reduction in water availability.

In other regions, changing rainfall patterns and
melting glaciers are altering river flow, causing a rise in
flooding. The SPM says:

"The fraction of global
population experiencing water scarcity and the fraction affected by
major river floods increase with the level of warming in the 21st
century."

Climate change is set to up the odds of the sort
of extreme weather the UK experienced this winter, scientists
say.

Sea level rise is projected to greatly increase
the risk of flooding in low-lying and coastal regions, particularly
in East, South and Southeast Asia.

The most visible impacts are on the natural
world

Warming is causing marine and terrestrial species to alter their
seasonal behaviour and to migrate into new geographical
territories. As surface waters warm, fish and invertebrates are
moving towards the poles or into deeper water in search of cooler
temperatures.

Redistribution of fish populations will have consequences for
food security and livelihoods in regions that depend on marine
resources. Falling productivity, ocean acidification and
overfishing will all contribute to the declining health of the
oceans out to 2100.

If species can't move or adapt fast enough, this
will lead to local extinctions. The SPM says:

"A large fraction of
both terrestrial and freshwater species faces increased extinction
risk under projected climate change during and beyond the 21st
century, especially as climate change interacts with other
stressors, such as habitat modification, over-exploitation,
pollution, and invasive species".

Ecosystems under pressure may cross critical
thresholds known as "tipping points", leading to abrupt and drastic
changes. The precise point at which tipping points are triggered is
uncertain, but there are already early warning signs of the Arctic
and coral reef systems undergoing irreversible regime
shifts.

Moderate warming in tropical and temperate
regions, like North America and Europe, will see decreases in the
major crop yields - wheat, rice and maize, though individual
locations may see short term benefits. After 2050 the risk of more
severe yield impacts increases. The SPM says:

"Based on
many studies covering a wide range of regions and crops, negative
impacts of climate change on crop yields have been
more common than positive impacts".

Impacts on food production are likely to hit rural communities
hardest and scientists expect a greater risk of malnutrition as
food production decreases in poor regions.

Changes in food production and quality will have
consequences for market prices and food security. The potential for
food shortages will be made worse by crop demand increasing 14 per
cent by 2050.

Climate change has other consequences for
human health

The number of people dying of heat-related
illnesses has increased in some regions, and will continue to rise
as the global population escalates.

As temperatures rise, there will be a modest
reduction in the number of people dying from cold in some areas,
which will offset some of the heat-related deaths.

Changes in temperature, sea level rise and
rainfall patterns have changed the distribution of disease vectors,
such as biting insects.

As southern Europe warms, the Asian Tiger mosquito
is moving towards northern countries in search of more suitable
habitat.

The frequency of injury, disease and death due
to more intense storms, floods and fires are expected to increase
in the next few decades. While climate change is and will continue
to be a contributor to poor global health, bigger causes of
ill-health exist around the world.

How much will climate change
cost?

Economists have attempted estimated the economic
cost of climate change by assessing the costs incurred as a result
of various different impacts. Existing estimates of the cost of 2.5
degrees of warming are between 0.2 and 2 per cent of
GDP.

The real economic costs of climate change will be higher than
estimates suggest, however. This is because they can't include
impacts without a monetary value attached, such as the decline in
biodiversity and loss of ecosystem services. The SPM says:

"Global economic impacts
from climate change are difficult to estimate. Economic
impact estimates completed over the past 20 years vary
in their coverage of subsets of economic sectors and depend on
a large number of assumptions, many of which are disputable".

Another important point is that very little is known about the
economic impacts above three degrees. The risks become much higher
above three degrees because of the potential for a large and
irreversible sea-level rise from ice sheet loss, the report
says.

Who will be most vulnerable?

The impacts of climate change are not evenly distributed across
the world. Developing countries and rural communities are likely to
be the hardest hit because of impacts to food production,
livelihoods and local economies. The SPM says:

"People who
are socially, economically, culturally, politically,
institutionally, or otherwise marginalized are often highly
especially vulnerable to climate change".

Climate change can exacerbate social and
economic inequalities, making vulnerable populations even more so.
As more people move to cities, the risks will become more
concentrated for a growing proportion of the global
population.

People living in places affected by violent
conflict or where access to food and water is already limited. In
some places, populations might be exposed to several impacts at the
same time - these are known as climate impact hotspots.

Adaptation can help manage risks from climate
change

Some of the risks posed by climate change can be
managed through adaptation. This involves minimising exposure to
the physical impacts while at the same time reducing vulnerability
through introducing climate-resilient infrastructure, ecosystem
restoration programmes, better water management, social and
sustainable development programmes, and livelihood
diversification.

For example, the new IPCC report says adaptation would lead to
an overall gain in crop yield of about 15 to 18 per cent of current
yields compared to the non-adaptation case, with the greatest
benefits for wheat, rice and maize in temperate regions rather than
tropical ones.

Adaptation can have co-benefits in terms of
alleviating poverty and enhancing development, particularly in
developing nations. There are still barriers to climate change
adaptation, particularly in developing countries, mainly because of
a lack of access to human and economic resources.

Making decisions in an uncertain
world

The report highlights there are a number of directions future
climate change and societal development could take. And the actions
we take now determine how much we're able to narrow those
possibilities.

The underlying message of the report is that
uncertainty about the scale, timing and location of physical
impacts shouldn't be a reason to delay on climate change
action.

Adaptation can reduce the impacts of climate change but it can't
avoid them altogether. So mitigation of carbon dioxide emissions is
important alongside adaptation, to reduce the scale of climate
impacts.

As well as reducing the cost of damage, a low
emissions pathway would also lower adaptation costs.

The final part of the IPCC report - from Working
Group 3 - deals with the topic of mitigation, and is due for
release in April 2014.